This application claims priority of Korea patent Application No. 10-2000-0056132, filed on Sep. 25, 2000.
(a) Field of the Invention
The present invention relates to a method for controlling an engine idle speed, and more particularly, to a method for controlling an engine idle speed by stopping ECU generation control for a short time and performing a feedback control of an engine speed in an early state of running.
(b) Description of the Related Art
Generally, the ECU (Electronic Control Unit) is supplied with data by various sensors installed in the engine and it operates an actuator, and thereby controls the engine.
In particular, when the ECU controls an ISC (Idle Speed Controller) in an idle state, the ECU is supplied with data like battery voltage, coolant temperature, a generation signal of an alternator that generates electricity, and it calculates engine load from the above data. When an instantaneous amount of air of the ISC is not sufficient with respect to engine load, the ECU controls the amount of air through the ISC to prevent a fluctuation of the engine speed.
To control the ISC according to an alternator output voltage in the idle state is called the ECU generation control. The ECU generation control prevents the engine speed from dropping down because of an instantaneous shortage of the amount of the ISC air. When performing the ECU generation control, the normal feedback control of engine speed stops for a short time (for example, for 2 seconds).
As an example of the ISC control, when a changed amount of alternator generation is larger than a predetermined value, the coolant temperature is higher than a predetermined temperature, an engine speed is lower than a predetermined speed, and engine intake manifold pressure is lower than a predetermined pressure, a compensated amount of air is calculated and the ISC is controlled such that a compensated amount of air is supplied to the engine. At this time, the normal feedback control of the engine speed is stopped for a predetermined period.
However, the above method for controlling the idle speed of the engine is also applied in an early running step when an operation of the engine is not stable.
In an early running step of the engine, the amount of alternator generation changes dramatically according to battery voltage and degree of electrical load.
At this time, if the ECU generation control according to the prior art is executed, the feedback control of engine speed is stopped for a given period, so even though the engine speed changes dramatically, it cannot be adequately controlled to a desirable speed and it becomes unstable for the given period. More seriously, the engine can stall, and especially when a coolant temperature is above a predetermined temperature, engine speed in an idle state is low and thus a possibility of stalling is greater still.
Therefore, the present invention relates to a method to solve the above problems, and an object of the present invention is to provide a method for preventing ECU generation control in the early state of running and for performing feedback control of engine speed.
To achieve the above object, the present invention provides a method for controlling idle speed that is used in an engine idle control system including a coolant temperature sensor, an alternator generation amount sensor, an engine speed sensor, an ISC controlling an amount of air supplied to the engine in an idle state, and an ECU that is supplied with detected values from the sensors and outputs a control signal to the ISC based on the supplied values, the method comprising the steps of:
determining whether time elapsed after starting is within a predetermined range; and
performing feedback control of engine speed in a state of stopping ISC control according to the amount of alternator generation when the time elapsed after starting is within the predetermined range.